The present invention relates to a parallel hybrid drive device that starts up an engine using a rotary, electric machine.
A so-called parallel hybrid drive device, which is well known in the art, includes a rotary electric machine coupled to an engine via a transfer clutch, a fluid power transmission device including a lock-up clutch and having a pump impeller and a turbine runner, and a transmission device coupled to the rotary electric machine via the fluid power transmission device to receive a driving force produced by one or both of the engine and the rotary electric machine each serving as a driving force source and to output the received driving force after changing the speed thereof.
In the parallel hybrid drive device, the engine is started from a so-called EV running state in which only a driving force produced by the rotary electric machine is output to run the vehicle, by transferring a part of the driving force produced by the rotary electric machine to the engine.
Such engine startup is performed, from a state in which a driving force is transferred from the rotary electric machine to the transmission device with the engine stationary, by executing rotational speed control in which the rotational speed of the rotary electric machine is brought to a target rotational speed with the lock-up clutch slipping, and engaging the transfer clutch. The rotational speed is synonymous with the number of revolutions.
Japanese Patent Application Publication No. JP-A-2007-326557 describes one form of such engine startup.
According to the technique described in Japanese Patent Application Publication No. JP-A-2007-326557, a lock-up clutch is allowed to slip at engine startup to control the rotational speed of a rotary electric machine such that a torque converter produces a certain rotational speed difference, and the torque capacity of the lock-up clutch is computed on the basis of a theoretical turbine torque calculated from the certain rotational speed difference and a target output torque, reducing a torque shock at engine startup.